If they hired you, you'd be competing with existing staff who are already doing the practical day-to-day work that they need done. These kind of hires that the

If they hired you, you'd be competing with existing staff who are already doing the practical day-to-day work that they need done. These kind of hires that the interviewee represents are about keeping people away from competitors. These companies - Facebook aren't the only one - are so rich that they can afford to hire people simply to reduce the chance that competitors will emerge; rather than waiting until you have to pay big money for Instagram or Whatsapp, you identify the kind of people who have the skills to build competitors, hire them, and lock them in a basement somewhere.